Niacin (Vitamin B3) Metabolism and Heart Disease
The GeneBank and CardioLipin studies measured niacin metabolism in a specialist referral setting. A niacin metabolite, 4PY, predicted future cardiac event risk. Mice exposed to synthetic 4PY showed elevated blood vessel inflammation.

This is a simplified look at a complex clinical trial. Full details are available at clinicaltrials.gov, the German Clinical Trials Register, and in the following publication:

 A terminal metabolite of niacin promotes vascular inflammation and contributes to cardiovascular disease risk | Nature Medicine 

Red meat plus Gut Microbes equals Heart Disease (The APPROACH Trial): 
The APPROACH trial tested in the community setting what already known in the laboratory setting: micro-organisms colonizing the colon mediate the relationship between red meat and cardiovascular disease.

This is a simplified look at a complex clinical trial. Full details are available at clinicaltrials.gov and in the following publications:

Fecal Microbiome Composition Does Not Predict Diet‐Induced TMAO Production in Healthy Adults | Journal of the American Heart Association (ahajournals.org)

The microbial gbu gene cluster links cardiovascular disease risk associated with red meat consumption to microbiota l-carnitine catabolism | Nature Microbiology 

 Effects of red meat, white meat, and nonmeat protein sources on atherogenic lipoprotein measures in the context of low compared with high saturated fat intake: a randomized controlled trial - ScienceDirect